1. Field of the Invention
The present invention relates to new polymers that have non-carbon tetravalent species (Si, Ti, Ge, Zr, Sn) and photoimageable compositions that contain such polymers. Preferred polymers are organic, e.g. one or more polymer repeat units comprise carbon atom(s). Particularly preferred are polymers that comprise SiO2 or TiO2 repeat units and which can be highly useful as a resin component of resists imaged at short wavelengths such as sub-300 nm and sub-200 nm.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
Photoresists are of particular interest that can be photoimaged with short wavelength radiation, including exposure radiation of about 300 nm or less, or 200 nm or less, such as wavelengths of about 248 nm (provided by KrF laser), 193 nm (provided by an ArF exposure tool), or 157 nm (provided by a F2 excimer tool). See European Published Application EP915382A2.
Use of such short exposure wavelengths can enable formation of smaller features. Accordingly, a photoresist that yields well-resolved images upon 248 nm, 193 nm or 157 nm exposure could enable formation of extremely small (e.g. sub-0.2 or 0.1 μm) features that respond to constant industry demands for smaller dimension circuit patterns, e.g. to provide greater circuit density and enhanced device performance.
In addition to using shorter wavelengths during exposure, it is also desirable to use a thinner layer of resist. However, the major drawback of using a thin layer of resist is that the variation of resist thickness over a diffusion step on a substrate and into an etched pattern increases as the pattern size becomes smaller. This variation means that the dimensions of any pattern being imaged in the resist will vary as the step geometry is traversed. Therefore, in a single layer resist system, the lack of dimensional control on the wafer can create different line widths throughout the resist which reduces the quality of the electronic package.
To attempt to improve dimensional control, bilayer (or bilevel or multilevel) resist systems have been utilized. In a typical bilevel system, a bottom resist is first applied to a substrate to planarize wafer topography. The bottom resist is cured and a second thinner imaging top resist is then applied over the bottom resist. The top resist is then soft baked, and patterned (or imaged) using conventional resist exposure and development, followed by etch transfer of the top pattern through the bottom resist using the top resist pattern as an etch mask. See Sugiyama et al., Positive Excimer Laser Resists Prepared with Aliphatic Diazoketones, Soc. Plastics Eng. Conference Proceedings, pages 51-60 (November 1988); and U.S. Pat. Nos. 4,745,169; 5,338,818; 5,619,396; 5,731,126; 6,296,985; and 6,340,734. See also WO 02/091083; U.S. Patent Publication 2002/0090572; and U.S. Pat. No. 5,378,585.
Certain inorganic Si compositions for imaging have been reported. See Fedynyshyn et al., Encapsulated Inorganic Resist Technology, Proceedings of SPIE, vol 3999, p. 627 (2000); Y. Hu et al., Nanocomposite resists for electron beam lithography, Microelectronic Engineering 56, 289 (2001); L. Merhai et al., Nanocomposite resists systems for next generation lithography, Microelectronic Engineering 1 (2002). These reported systems are currently not practical for high performance applications.
A problem associated with the thin-layer bi-layer resist systems is to provide acceptable transparency to exposure radiation as well as good resistance to plasma etchants. This is particularly an issue for bi-layer resists that are imaged at sub-200 nm wavelengths such as 193 nm and 157 nm. See US Published Application 2003/0207205 and U.S. Pat. No. 6,593,058, where efforts at increasing etch resistance of bi-layer resists are reported.
It would be desirable to have new photoresists that could provide small images of high resolution. It would be particularly desirable to have new photoresists that could be effectively imaged with short wavelength radiation, including sub-300 nm such as 248 nm and sub-200 nm radiation such as 193 nm and 157 nm. It would be further desirable to have such photoresists that exhibited plasma etch resistance and good transparency to short exposure wavelengths such as 193 nm and 157 nm.